1. Field of the Invention
The present disclosure relates to a fuel cell.
2. Discussion of the Background
For example, a solid polymer electrolyte fuel cell, which is a power generation cell, includes a membrane electrode assembly (MEA) and a pair of separators sandwiching the MEA therebetween. The MEA includes a solid polymer electrolyte membrane, which is a polymer ion-exchange membrane, and an anode electrode and a cathode electrode sandwiching the solid polymer electrolyte membrane therebetween. A fuel cell stack, which usually includes a plurality of power generation cells that are stacked, is used in a stationary usage or used as a vehicle fuel cell system mounted in a fuel cell vehicle.
In the fuel cell, a fuel gas channel (also referred to as a reactant gas channel), through which a fuel gas flows to the anode electrode, is formed on a surface of one of the separators; and an oxidant gas channel (also referred to as a reactant gas channel), through which an oxidant gas flows to the cathode electrode, is formed on a surface of the other separator. Moreover, for each power generation cell or for a group of power generation cells, a coolant channel, through which a coolant flows, is formed along a surface of a separator.
In such a fuel cell, it is necessary to humidify the electrolyte membrane in order to keep good ion conductivity. Therefore, an oxidant gas (for example, air) and a fuel gas (for example, hydrogen gas), which are reactant gases, are humidified and supplied to the fuel cell.
Water used for moisturizing the electrolyte membrane may not be absorbed by the electrolyte membrane and liquid water may accumulate in the reactant gas channel. In the fuel cell, water is generated in the cathode electrode due to a power generation reaction, and the generated water is back-diffused to the anode electrode through the electrolyte membrane. Therefore, water may condense and accumulate in the reactant gas channel. Therefore, in particular, on the cathode electrode side, which has a higher electric potential, a metal may leach into accumulated water and the metal may be trapped into the electrolyte membrane. Thus, there is a problem in that the electrolyte membrane deteriorates rapidly due to metal ions.
For example, Japanese Unexamined Patent Application Publication No. 5-21077 discloses a sealing structure to address this problem. As illustrated in FIG. 17, the sealing structure is incorporated in a solid polymer electrolyte fuel cell 1.
The fuel cell 1 includes an MEA 2 including a solid polymer electrolyte membrane 2a sandwiched between an anode electrode 2b and a cathode electrode 2c. The MEA 2 is sandwiched between an anode separator 3, on which a fuel channel 3a is formed, and a cathode separator 4, on an oxidant channel 4a is formed.
In the MEA 2, the solid polymer electrolyte membrane 2a has a surface area that is larger than that of each of the anode electrode 2b and the cathode electrode 2c. Frame-like protection films 5 are disposed on both surfaces of a peripheral portion of the solid polymer electrolyte membrane 2a. 
Outer peripheral portions of the protection films 5 include portions that overlap the outer peripheries of the anode electrode 2b and the cathode electrode 2c. A pair of gas sealing members 6, each having a frame-like shape, are disposed in the outer periphery of the anode electrode 2b and the cathode electrode 2c. 
Thus, the outer peripheral portions of the protection films 5, which are fixed to the solid polymer electrolyte membrane 2a, are sandwiched between the pair of gas sealing members 6; and inner peripheral portions of the protection films 5 are sandwiched between the anode electrode 2b and the cathode electrode 2c. Therefore, the solid polymer electrolyte membrane 2a is prevented from becoming damaged and can have gas sealability.